1. Field of the Invention
This invention relates generally to sheet material article feeders, and more specifically to feeders which feed one article at a time from the bottom of a stack of sheet articles.
2. Prior Art and Other Considerations
Sheet feeders which feed from the bottom of a stack often employ endless feed belts having a feeding surface contacting the bottom face of the lowermost sheet and thereby driving the sheet substantially in and along its plane from beneath the stack. Such sheet article feeders commonly employ a restraining structure or mechanism to block and prevent all but the lowermost sheet from being passed therethrough.
Difficulties encountered with conventional feeders have included misfeeds in form of double or multiple sheets being fed or, alternately, absences of a sheet when it should have been fed. These difficulties are experienced particularly in high speed operation and when sheet articles of differing properties are handled. For instance, different material thickness, stiffness, surface friction, and different sheet article sizes have critically affected reliable operation of such feeders in the past. Sensitive mechanical adjustment has been generally required to particular sheet article properties and sizes to assure reliable operation, and even relatively slight changes in such properties and/or sizes necessitated readjustment of the device. Consequently, such feeders have also been unable to reliably handle a mix of sheet articles.
Prior art feeders singulating and feeding individual sheets from the bottom of a stack have employed a variety of restrainer or retarder mechanism in order to prevent all but the lowermost sheet to be fed. Such feeders are, for example, shown in the following U.S. Patents.
Rouan (U.S. Pat. No. 2,273,288) discloses an adjustable separator for stripping letters from the bottom of a stack. Adjustment facilitates substantially constant tension whilst the separator yields as letters of varying thickness pass therebeneath. Kramell et al (U.S. Pat. No. 3,895,791) discloses a bottom sheet feeder comprising a separation belt and a retard pad that is biased against the belt to bow the belt down. Strobel (U.S. Pat. No. 3,934,869) shows a sheet separating and feeding apparatus including a feed belt adapted for frictional engagement with retard means 38. Generally similar devices are also shown by Godlewski and by Larson in U.S. Pat. Nos. 4,666,140 and 4,555,103, respectively.
Imposition of transverse bowing onto sheet materials for various purposes during sheet handling and transporting is shown in prior art, for instance, by U.S. Pat. No. 4,744,555 to Naramore et al, U.S. Pat. No. 4,663,527 to Koyama et al, and U.S. Pat. No. 2,157,228 to Buccicione et al.
The sheet article feeder of the present invention particularly obviates difficulties of the aforementioned kind and provides reliable singulating and feeding of sheet material from the bottom of a stack in high speed operation and for sheet material that can vary significantly in properties as well as size. The sheet article feeder tolerates substantial misalignments of individual articles (including skew) without misfeeding and without the need for adjustments to accommodate different and mixed different sheet materials in uninterrupted operation. These characteristics provide significant operating and cost advantages not heretofore provided by prior art devices.
Accordingly, an important overall feature of the invention is the provision of an improved sheet material feeder and an improved method of singulating and feeding thereby sheet material of different and mixed properties and sizes from the bottom of a stack disposed in a hopper, the feeder including means for urging sheets in the stack toward a singulating exit region and means for feeding a lowermost sheet from the stack through a restrainer device, wherein the restrainer device restrains all but the lowermost sheet from feeding out from the hopper by virtue of transversely resiliently corrugating the lowermost sheet while it passes through the restrainer device.